Film driving apparatus



NOV. 4, 1947. Q c. DAVls FILM DRIVING APPARATus' Filed June 26, 1945 2 Sheets-Sheet 1 I m A ND C W A TTORNEY Nov. 4, 1947.

c. c. DAVIS 2,429,995

FILM DRIVING APPARATUS Filed June 26, 1945 2 Sheets-Sheet 2 FIG. 3

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INVENTOR C. 6. DA V/S A TTORNE Y Patented Nov. 4, 1947 2,429,995 FILM DRIVING APPARATUS Charles C. Davis, West Los Angeles, Calif; as-

signor to Western Electric Company, Incorporated, New York, N. Y., a corporation of New York Application June 26, 1945, Serial No. 601,697 3 Claims. (01. 271-223) This invention relates to a sound film propulsion mechanism and more-particularly to improvements in mechanical filtering systems employed in such mechanism to suppress oscillations produced in the film by the film driving element.

It is the object of this invention to provide in a sound film propulsion mechanism an improved filtering system by means of which flutter produced in the film by the film driving element is efficiently suppressed at the sound recording or reproducing point.

It is a further object of this invention to provide as an element of the filter system an improved damping roller assembly afiording a maximum of accessibility and dependability whereby the filter elements of the damping assembly may be readily adjusted and maintained in adjustment over long periods.

A feature of the invention resides in the provision of a damping roller assembly comprising a base on which is mounted a spring-urged, pivoted arm carrying a film-engaging roller and the plunger element of an oil dash-pot carried by the base, the assembly being so constructed that the characteristics of the spring and dash-pot filter elements do not vary appreciably from their optimum value with displacement of the film-engaging roller from its mean position.

The invention will be more readily understood from the followingspecification when read in connection with the accompanying drawings in which:

Fig. 1 is a side elevation of a sound film reproducing apparatus showing the arrangement of film propelling and guiding element in accordance with this invention;

Fig. 2 shows a circuit having electrical element equivalent to the physical elements of the film driving mechanism of Fig. 1;

Fig. 3 is an enlarged plan view of the damping roller assembly of Fig. 1;

Fig. 4 is a section taken through line 4-4 of Fig. 3;

Fig. 5 is a section taken through line 5-5 of Fig. 4;- and Fig. 6 is a section taken through line 6--6 of Fig. 4. Referring to Fig. 1, numeral I indicates a housing for a sound film reproducing apparatus. This housing is divided into two compartments 3 and 4. Compartment 3, enclosed by hinged door 5,

contains the usual' exciter lamp and associated electrical equipment. Compartment 4 contains the film driving and guiding elements and the .optical system of the sound film reproducing apparatus. A hinged door 5 is provided for this compartment.

A film F, having a photographic sound record adjacent one marginal edge thereof, is fed through an opening in the top of the housing i from a feed reel or from the driving sprocket of a picture reproducing mechanism with which the sound reproducer may be associated.

The film F engages a scanner drum 1 with the sound record edge thereof overhanging the near edge of the drum. On the incoming side of the drum. the film is held in engagement therewith by a pressure roller 8 mounted on an arm 9 pivoted to the housing at pivot point ID. A portion of the arm 9 is formed by leaf spring Ii which resiliently'urges the roller 8 against the film or drum 1.

The overhanging sound record portion of the film F is disposed in a reproducing optical system comprising a condenser lens tube l2 which extends into compartment 3 to receive light from the exciting lamp disposed therein and an objective lens system included in a lens tube l3 which projects an enlarged image of the sound record to a fixed slit disposed in front of a reproducing photoelectric cell located in compartment H with its associated amplifier.

The scanner drum I is engaged and driven by the film F. A flywheel I5 is mounted on the shaft of the scanner drum 1 for rotation therewith. A narrow metal cylinder l6 attachedto and extending axially of the flywheel l5 forms one element of a magnetic damping mean associated with here that the roller 20 is rotatably mounted on the flywheel. A permanent magnet I1 is secured to flywheel housing [8 in a manner to place its poles adjacent the path of rotation of the metal cylinder l6. While a single permanent magnet is disclosed, it will be understood that additional magnets may be employed depending upon the amount of magnetic drag desired.

After leaving the scanner drum 1, the film engages a roller 20 which is rotatably mounted on a shaft 2|. The damping roller assembly associated with roller 20 will be described in greater detail hereinafter. It is suficient to point out an arm 22 which is pivoted on base 23 at pivot 24. The arm '22 is resiliently urged toward the film by a coil spring 25. Movement of the arm and 'roller about its pivot is damped by an oil dashpot located at 26. The damping roller unit assembly is secured to the inner wall of compartment 4 by machine screws 21 and 28 extending through base 23.

trical elements equivalent to The film. F is engaged and driven by constant speed sprocket 35. A take-up sprocket 8i engages and drives the film to a suitable take-up reel (not shown). Pivoted rollers 32 and 33 retain the film F on sprockets 30 and 3i, respectively.

Fig. 2 shows an electrical circuit having electhe physical elements of the film drive disclosed in Fig. 1. The inductance L1 is the equivalent of the combined mass of the scanner drum 1 and its associated flywheel l5. .Resistance R2 is the equivalent of the resistance of the magnetic braking provided by the metal cylinder I6 and the permanent magnet l1. Capacity C2 is the equivalent of the compliance of the film between the scanner drum I and the constant speed drive sprocket 30. The inductance L2, capacity C1 and the resistance R1 are equivalent respectively to the combined mass of roller '20 and pivoted arm 22, the compliance ofspring 25 and the fluid friction damping of oil dash-pot 26. Inductance L3 is the equivalent of themass of sprocket 30 while D represents a source of alternating current or flutter velocity introduced in the circuit or film drive by sprocket mass 30.

The filter circuit as shown in Fig. 2 may be considered as a circuit consisting of three branches and receiving a, constant current (velocity) from the motor driven sprocket 30 represented by the inductance L3. The inductance L1 constitutes one branch of the circuit. The capacity C2 (film comipliance) constitutes a second branch, while the third branch is formed by the impedance across the circuit made u of the inductance L2, capacity C1 and resistance R2.

It is the purpose of a filter system of this type to suppress alternating current (flutter velocity) at the inductance L1. The point of interest therefore is the relative effect at the scanner drum 1 when a disturbance is introduced at the drive sprocket 30.

Frequency disturbances throughout the greater portion of the range of disturbing frequencies likely to b introduced at sprocket 30 are attenuated effectively by the drum and flywheel mass (L1) and the film compliance (C2). However, the filter system formed by the drum and flywheel mass 'L1 and the film compliance approaches resonance at a relatively low frequency within this frequency range and, therefore, this filter becomes inefiective fonattenuating disturbing frequencies near the resonance frequency and below,

Lower frequency disturbances introduced by the film driving elements are attenuated by the filter system provided by the flywheel mass and the damping roller or, that constituted by the combined mass of the flywheel l5, drum 1 and roller arm 22 (L1, La) and the compliance of the spring 25 (C1). The oil dashpot 26 (R1) is introduced to prevent a high peak or an actual increase in the transmission of the resonant frequency of this filter system at approximately onehalf cycle.

One of the principal functions of the magnetic damping produced by magnet I1 and cylinder l6 (R2) is to decrease the film compliance (C2) to a point where it is much smaller than the amped compliance of spring 25 (C1) thus permitting the compliance of spring 25 (C1) and the resistance damping of oil dash-pot 26 (R1) to control the resonant peak of the mass L1 and the compliance C1. As a result of this action, the percentage change in film compliance (C2) due to bending and other causes produces less total change in the L2, (T31, R1 :branch in the scanner branch of the 'the values selected for thefilter elements should remain constant. Where, in a mechanical system the equivalent of the electrical inductance,

' capacity and resistance are supplied by mass,

spring compliance and magnetic or fluid friction damping, the problem is presented of providing a mechanical structure in which the spring compliance will be maintained substantially uniform regardless of stretching of the spring with displacement of the roller carrying arm during operation and in.which static friction at the pivot bearing and changes in fiuid friction of the oil dash-pot for various reasons will be sufiiciently minimized to prevent noticeable deterioration of the desired filter action with normal operation of the mechanical filter system.

In accordance with this invention there is provided a damping roller assembly incorporating novel structural features and arrangement of elements in which the possibility of variation in the characteristics of the filter elements with normal and intended operation of the damping roller is greatly reduced.

Referring to Fig. 3 a boss 40, extending from the inner wall 4| of compartment 4, provides a mounting surface for the unit assembly damping roller of which the 40' by means of machine screws 2! and 28. The base 23 isprovided with three upwardly extending end sections 43, 44 and 45. Sections 43 and 45 are each provided with a threaded hole to receive externally threaded pivot bearings 24 and 46, respectively. The sections 43 and 45 are each split, as shown in Figs. 3 and 4, and by means of machine screws 48 and 49 the pivot bearings 24 and 46 may be clamped in adjusted position.

A relatively long arm 22 is pivoted from the base 23 at the pivot bearings 24 and 26 Referring particularly to Fig. 5, the pivoted end of arm 22 is provided with ball bearings 56 and 5| which engage the pivot bearings 24 and 26, respectively, the pivot bearings forming the inner race of the ball bearing in each instance. It will be noted from this figure that the roller carrying arm may be adjusted laterally by movement of the pivot bearings within the limits permitted by a stop formed by the end section 44 of base 23.

The roller carrying end of arm 22 terminates in an inverted cylindrical cup 52. Referring particularly to Fig. 6, the shaft 2| is fixedly mounted in the base of the cup-shaped end 52 of arm 22. The film engaging rollers 20 are rotatably mounted on shaft 2|. Each roller 20 forms the outer race of a ball bearing, the inner race 53 of which is clamped to shaft 2| by the fiange of machine screw 54 which engages an internal thread in shaft 2|.

The provision of a ball bearing at the pivot of arm 22 and for the rollers 20 substantially eliminates the possibility of variations in the characteristic of the mechanical filter due to the introduction of a non-uniform resistance component likely to be produced by static friction in the bearings.

A rod 56, extending downwardly from and normal tothe axis of shaft 2|, is secured in the base of cup 52. To the free end of rod 56 there is secured a circular plunger 51.

The fluid-filled dash-pot 26 is removably mounted in the base 23 in the path of movement of the plunger 51. An external thread 58 on the base 23 is secured to the boss dash-pot engages an internal thread 59 on the base 23. The lower part of dash-pot 55 is provided with a flange 60 having a knurled surface to permit ready removal of the dash-pot from the base 23 for inspection of or replacement of the damping fluid therein.

By providing a relatively long pivoted arm 22. the film-engaging roller 20 travels substantially in a straight line path during normal movement in response to tension variations in the film.

' Disposition of the plunger 51 directly below the axis of roller 20 provides the advantage that as the plunger travels the same distance as the roller and in substantially the same straight line path,

the clearance between the plunger and the inner surface of the oil dash-pot will not vary during its travel, thereby insuring uniform damping or an unvarying value of the equivalent electrical resistance R1.

Referring particularly to Figs. 4 and 5, a rod 62 is secured to the arm 22 at its pivot. One end of coil spring 25 is secured to the free end of rod 62. The other end of coil spring 25 is secured to one end of rod 62, the opposite end of which extends through a hole in base 23 and is provided with a screw thread. A nut 64 engaging the threaded end of rod 63 provides means for adjusting the initial tension of spring 25. The nut 64 may be locked in adjusted position by means of set screw 65.

The arrangement of the spring 25 in the base of the assembly in parallel relation to the pivoted arm in its mean position and with the spring engaging the arm at its pivot, permits the use of a relatively long, soft spring (large compliance) in which the spring tension does not vary appreciably from its adjusted optimum value with change in its length during operation. Therefore, there is provided a mechanical filter element equivalent to the electrical capacity C1 whose variations from optimum value are greatly minimized.

A further advantage to be realized in the construction of the damping roller in accordance with this invention is that the oil in the dash-pot is protected from dust and other foreign particles which produces a change in its viscosity. The cover formed by the inverted cup-shaped end 52 of arm 22, which operates in telescoping arrangement with the oil cup 26, provides this protection.

An upper movement limiting stop for the pivoted arm 22 is provided by the head of bolt 86 secured in adjusted position in base 23 by a nut 61.

What is claimed is:

1. The combination in a film-propellingapparatus having a film-driven drum and sprocket means for driving said film, of a mechanical filtering means engaging said film between said drum and said sprocket, said means comprising a base, an arm having one end pivoted on said base, and its free end terminating in an inverted cylindrical cup, a cylindrical aid-carrying container removably mounted in said base and extending upwardly into the cup-shaped end of said arm in telescoping relation therewith, a plunger extending into said fiuid container and secured to said pivoted arm centrally of the cup-shaped end thereof and a rotatable film-engaging roller mounted on said arm externally of the base of the cup-shaped end thereof, with its axis of rotation extending through and normal to the axis ofsaid plunger.

2. The combination in a film propelling apparatus having sprocket means for driving said film, of a damping roller assembly comprising a base, an arm having one end pivoted on said base, and its free end terminating in an inverted cup, a downwardly extending plunger secured to said arm centrally of said cup, a rotatable film-engaging roller mounted on said arm externally of the base of the cup-shaped end thereof, a fluid-carrying container mounted in said base and extendin upwardly into the cup-shaped end of said arm in telescoping relation therewith, and adjustable pivot bearings for said arm permitting lateral movement thereof to properly locate said plunger with respect to said fluid-carrying container.

3. The combination in a film propelling apparatus having a sprocket means for driving said film, of a mechanical filtering means engaging said film, said means comprising a base, an arm REFERENCES CITED The following references are of record in the file of this patent:

, UNITED STATES PATENTS Number Name Date 2,033,611 Chidester Mar. 10, 1936 Re. 19,270 Kellogg Aug. 14, 1934 1,972,456 Newman et a1. Sept. 4, 1934 

